Latino adolescents in the U.S. are at higher risk of contracting STDs than European American adolescents, partially because of their lower rates of condom use. Condom use is a complex behavior. Because it is under the physical control of males, the dynamics between sexual partners are critical to effective use. This study will use qualitative and quantitative methods to examine the impact of sexual relationship dynamics on condom use among Mexican American and Central American adolescent heterosexual partners. The research will include both sexual partners. Based on a theoretical framework for relationship power and informed by our own previous work, we will examine how relationship power influences condom use among adolescents who disagree about whether or not to use condoms. We will examine whether sexual partners' relative personal resources (e.g., emotional investment in the relationship) and the influence strategies that each partner uses are related to actual condom use. We will also examine how specific elements of the cultural context (gender role beliefs, sexual comfort, comfort with sexual communication, and concern about negative responses) are linked to the influence strategies that Latino adolescents use to obtain condom use. Finally, through individual qualitative interviews with a subgroup of sexual partners who disagree about whether or not to use condoms, we will obtain a full description of relationship dynamics that relate to condom use. In this 5-year cross-sectional study, we will recruit 552 Mexican American and Central American adolescents, ages 16-20, and their sexual partners, from the membership of a large HMO. We will conduct qualitative interviews with 100 primary participants and their sexual partners who disagree about whether to use condoms. The proposed research is among the first empirical studies to examine how relationship dynamics such as relative power and influence strategies are related to condom use among Latino adolescents. It is also among the first studies of HIV risk behavior to include both sexual partners, an approach that will provide more complete information about relationship dynamics, and will facilitate the development of couple-based interventions. The results will provide critical information to refine STD/HIV interventions that teach safer sex negotiation skills, and to develop culturally appropriate interventions for Latino adolescents.